Heretofore, as this sort of picture coding apparatus, there is such a device that hierarchically codes an input picture data using a hierarchical coding scheme such as the pyramidal coding scheme (Japanese Patent Publication No. 142836/1993). In this picture coding apparatus, the high resolution input picture data is treated as the first hierarchy data, and the second hierarchy data which has a lower resolution than the first hierarchy data, the third hierarchy data which has a lower resolution than the second hierarchy data, . . . are formed sequentially and recursively, and these plural hierarchy data are transmitted through a transmission line which is composed of one communication channel or a recording/reproducing path.
A picture decoding device which decodes the plural hierarchy data is able to decode all of the plural hierarchy data, and also is able to select and decode the desired one out of the hierarchy data, based on the resolution of a corresponding television monitor and the like. By decoding only the desired hierarchy data out of thus hierarchized plural hierarchy data, the desired picture data can be obtained, with the irreducible minimum of transmitting data quantity.
As shown in FIG. 1, the picture coding apparatus which realizes this hierarchical coding such as a four hierarchy coding has decimating filters 2, 3, 4 and interpolating filters 5, 6, 7 both for three stages, and progressively forms the compacted picture data D2, D3, D4 of which the resolutions are low by the decimating filters 2, 3, 4 of each stage with respect to the input picture data D1, and returns the resolutions of the compacted picture data D2, D3, D4 to the former resolution prior to the compaction by the use of the interpolating filters 5, 6, 7.
The output D2 to D4 of respective decimating filters 2 to 4 and the output D5 to D7 of the respective interpolating filters 5 to 7 are inputted into the difference circuit 8, 9, 10 respectively, hereby the difference data D8, D9, D10 is generated. As a result, in the picture coding apparatus 1, the data quantity of the hierarchical data is reduced and the signal power is reduced. The sizes of the difference data D8, D9, D10 and the compacted picture data D4 are 1, 1/4, 1/16, and 1/64 times the size of the input picture data D1 in area, respectively.
The difference data D8 to D10 which are obtained from the respective difference circuit 8 to 10 and the compacted picture data D4 which is obtained from the decimating filter 4 are compressed by respective coders 11, 12, 13, 14. As a result, the first, the second, the third, and the fourth hierarchy data D11, D12, D13, and D14 which have different resolutions are sent out, in the stated order, from the respective coders 11, 12, 13, 14 to the transmission line.
The first to the fourth hierarchy data D11 to D14 which are transmitted in this manner are decoded by a picture decoding apparatus shown in FIG. 2. The first to the fourth hierarchy data D11 to D14 are decoded by decoders 21, 22, 23, 24 respectively. As a result, the fourth hierarchy data D24 is outputted from the decoder 24 first.
At the adding circuit 29, the output of the decoder 23 is added to the interpolated data of the fourth hierarchy data D24 which is obtained from the interpolating filter 26, hereby the third hierarchy data D23 is restored. Similarly, at the adding circuit 30, the output of the decoder 22 is added to the interpolated data of the third hierarchy data D23 which is obtained from the interpolating filter 27, hereby the second hierarchy data D22 is restored. Furthermore, at the adding circuit 31, the output of the decoder 21 is added to the interpolated data of the second hierarchy data D22 which is obtained from the interpolating filter 28, hereby the first hierarchy data D21 is restored.
In the picture coding device which realizes such a hierarchical coding method, the input picture data is divided into the plural hierarchy data and coded, therefore the data quantity is inevitably increased by the amount of the hierarchy component. Consequently, there is a problem that the compression efficiency is lowered for the amount of the increasing, in comparison with a high efficiency coding method which does not utilize the hierarchical coding. Besides, there is a problem that in the case where the improvement of the compression efficiency is aimed, the deterioration of picture quality is induced, due to the quantizer which is applied between each hierarchy data.